This patch implements a "flash friendly" value for initialized areas of flash.

This patch implements a "flash friendly" value for initialized areas of flash.
It makes the write part of flashrom dramatically faster with small
payloads like filo; and it also eliminates unnecessary wear on flash
by not writing zeros (it's unlikely this really matters; let me know
next time you flash a BIOS flash 100,000 times!).

More importantly, it allows for future partial flash upgrades with cbfs.

Note that uninitialized_flash_value is a global that can, if we ever need it,
be set by an argument in main. Assuming we ever see a flash where the
"erased" value is 0, not 0xff.

At the same time, "erased" value has been "1" on every EEPROM or
FLASH I've used for some time now.

Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Acked-by: Peter Stuge <peter@stuge.se>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@4290 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1